Storage medium for data with improved dimensional stability

ABSTRACT

This disclosure relates to a data storage medium, and in particular to a data storage medium comprising at least one high modulus layer used to control the overall degree of flatness in the storage medium.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of the filingdate of U.S. Provisional application No. 60/316,534, filed Aug. 31, 2001and entitled STORAGE MEDIUM FOR DATA.

BACKGROUND OF INVENTION

[0002] This disclosure relates to a data storage medium, and inparticular to a data storage medium comprising at least one high moduluslayer used to control the overall degree of flatness in the storagemedium.

[0003] An increase in data storage density in optical data storage mediais desired to improve data storage technologies, such as, but notlimited to, read-only media, write-once media, rewritable media, digitalversatile media and magneto-optical (MO) media.

[0004] As data storage densities are increased in optical data storagemedia to accommodate newer technologies, such as, but not limited to,digital versatile disks (DVD) and higher density data disks for shortand long term data archives such as digital video recorders (DVR), thedesign requirements for the transparent component of the optical datastorage devices have become increasingly stringent. Optical disks withprogressively shorter reading and writing wavelengths have been theobject of intense efforts in the field of optical data storage devices.Materials and methods for optimizing physical properties of data storagedevices are constantly being sought. Design requirements for thematerial used in optical data storage media include, but are not limitedto, disk flatness (e.g., tilt), water strain, low birefringence, hightransparency, heat resistance, ductility, high purity, and mediumhomogeneity (e.g., particulate concentration). Currently employedmaterials are found to be lacking in one or more of thesecharacteristics, and new materials are required in order to achievehigher data storage densities in optical data storage media. Diskflatness, also referred to as tilt, is a critical property needed forhigh data storage density applications. Consequently, a long felt yetunsatisfied need exists for data storage media having improveddimensional stability and minimal tilt.

SUMMARY OF INVENTION

[0005] In one embodiment, the present disclosure is drawn to anasymmetric optical storage medium comprising a layer, which improvesdimensional stability in said medium, wherein the asymmetric opticalstorage medium comprises at least one substrate layer, at least one datalayer, at least one high modulus layer, and at least one thin filmlayer.

[0006] In another embodiment, the present application is drawn to amethod for decreasing the tilt of an asymmetric optical storage medium,said method comprising an addition step wherein a high modulus layer isadded to an optical storage medium so that the directional stability ofsaid medium is increased.

BRIEF DESCRIPTION OF DRAWINGS

[0007] Various features, aspects, and advantages of the presentdisclosure will become apparent with reference to the following detaileddescription, appended claims, and accompanying figures.

[0008]FIG. 1 is a cross sectional view of one embodiment of the presentdata storage medium (10), wherein the medium comprises a substrate layer(20), which is in direct contact with a data layer (30), a data layer(30), which is in direct contact with a thin film layer (40), and a thinfilm layer (40), which is in direct contact with a high modulus layer(50).

[0009]FIG. 2 is a cross sectional view of another embodiment of thepresent data storage medium (60), wherein the medium comprises asubstrate layer (70), which in direct contact with a data layer (80), adata layer (80), which is in direct contact with a high modulus layer(90), and a high modulus layer (90), which is in direct contact with athin film layer (100).

DETAILED DESCRIPTION

[0010] The present disclosure describes the use of polymeric material asstorage media for data. In one embodiment of the present disclosure, thestorage medium for data (part 10 in FIG. 1; part 60 in FIG. 2) comprisesa plurality of layers comprising at least one substrate layer, at leastone data layer that is in direct contact with the substrate layer, atleast high modulus layer, and at least one thin film layer. As usedherein, the term “high modulus” refers to a tensile modulus typicallygreater than about 1 Gigapascal (Gpa). The high modulus layereffectively increases the dimensional stability of the data storagemedium by reducing the tilt of the data storage medium. As used herein,the term “tilt” refers to the number of radial degrees by which a datastorage medium bends on a horizontal axis, and is typically measured asthe vertical deviation at the outer radius of the storage medium.Typically, the tilt is half of the average radial deviation (thedeviation of a laser beam) as measured in degrees.

[0011] In the context of the present disclosure, a typical data storagemedium is composed of a plurality of polymeric components, which aregenerally combined in overlaying horizontal layers of variousthicknesses, depending on the specific properties and requirements ofthe data storage medium. A major component of a data storage medium is asubstrate layer (part 20 in FIG. 1; part 70 in FIG. 2). The substratelayer is typically made of a polymeric material, which comprises atleast one member selected from the group consisting of a thermoplastic,a thermoset, and any combination thereof. Both addition and condensationpolymers are suitable for the present invention. As used herein the term“thermoplastic polymer”, also referred to in the art as a thermoplasticresin, is defined as a material with a macromolecular structure thatwill repeatedly soften when heated and harden when cooled. Illustrativeclasses of thermoplastic polymers include, but are not limited to,styrene, acrylics, polyethylenes, vinyls, nylons, and fluorocarbons. Asused herein the term “thermoset polymer”, also referred to in the art asa thermoset resin, is defined as a material which solidifies when firstheated under pressure, and which cannot be remelted or remolded withoutdestroying its original characteristics. Illustrative classes ofthermoset polymers included, but are not limited to, epoxides,malamines, phenolics, and ureas.

[0012] Illustrative examples of thermoplastic polymers which aresuitable for the substrate layer include, but are not limited to,olefin-derived polymers (e.g., polyethylene, polypropylene, and theircopolymers), polymethylpentane; diene-derived polymers (e.g.,polybutadiene, polyisoprene, and their copolymers), polymers ofunsaturated carboxylic acids and their functional derivatives (e.g.,acrylic polymers such as poly(alkyl acrylates), poly(alkylmethacrylates), polyacrylamides, polyacrylonitrile and polyacrylicacid), alkenylaromatic polymers (e.g., polystyrene,poly-alpha-methylstyrene, polyvinyltoluene, and rubber-modifiedpolystyrenes), polyamides (e.g., nylon-6, nylon-6,6, nylon-1,1, andnylon-1,2), polyesters; polycarbonates; polyester carbonates; polyetherssuch as polyarylene ethers, polyethersulfones, polyetherketones,polyetheretherketones, polyetherimides; pqlyarylene sulfides,polysulfones, polysulfidesulfones; and liquid crystalline polymers. Inone embodiment, the substrate layer comprises a thermoplastic polyester.Suitable examples of thermoplastic polyesters include, but are notlimited to, poly(ethylene terephthalate), poly(1,4-butyleneterephthalate), poly(1,3-propylene terephthalate),poly(cyclohexanedimethanol terephthalate), poly(cyclohexanedimethanol-co-ethylene terephthalate), poly(ethylenenaphthalate), poly(butylene naphthalate), and polyarylates.

[0013] In another embodiment the substrate layer comprises athermoplastic elastomeric polyesters (TPE”s). As defined herein, athermoplastic elastomer is a material that can be processed as athermoplastic material, but which also possesses some of the propertiesof a conventional thermoset resin. Suitable examples of thermoplasticelastomeric polyesters include, but are not limited to, polyetheresters,poly(alkylene terephthalate), poly[ethylene terephthalate], poly[butylene terephthalate]), polyetheresters containing soft-blocksegments of poly (alkylene oxide) particularly segments of poly(ethyleneoxide) and poly(butylene oxide), polyesteramides such as thosesynthesized by the condensation of an aromatic diisocyanate withdicarboxylic acids, and any polyester with a carboxylic acid terminalgroup.

[0014] Optionally, the substrate layer can further comprise at least onedielectric layer, at least one insulating layer, or any combinationsthereof. The dielectric layer(s), which are often employed as heatcontrollers, typically have a thickness between about 200 Å and about1,000 Å. Suitable dielectric layers include, but are not limited to, anitride layer (e.g., silicone nitride, aluminum nitride), an oxide layer(e.g. aluminum oxide), a carbide layer (e.g., silicon carbide), and anycombinations comprising at least one of the foregoing and any compatiblematerial that is not reactive with the surrounding layers.

[0015] In the context of the present disclosure, a typical data storagemedium further comprises at least one data layer (part 30 in FIG. 1;part 80 in FIG. 2). The data layer, which typically comprises areflective metal layer, can be made of any material capable of storingretrievable data, such as an optical layer, a magnetic layer, amagneto-optic layer. The thickness of a typical data layer can be up toabout 600 Angstroms (Å). In one embodiment, the thickness of the datalayer is up to about 300 Å. The information which is to be stored on thedata storage medium can be imprinted directly onto the surface of thedata layer, or stored in a photo-, thermal-, or magnetically-definablemedium which has been deposited onto the surface of the substrate layer.Suitable data storage layers are typically composed of at least onematerial selected from the group consisting of, but are not limited to,oxides (e.g., silicone oxide), rare earth element-transition metalalloys, nickel, cobalt, chromium, tantalum, platinum, terbium,gadolinium, iron, boron, organic dyes (e.g., cyanine or phthalocyaninetype dyes), inorganic phase change compounds (e.g., TeSeSn or InAgSb),and any alloys or combinations comprising at least one of the foregoing.

[0016] The reflective metal layer(s) should be of a thickness that issufficient to reflect an amount of energy, which is sufficient to enabledata retrieval. Typically, a reflective layer has a thickness up toabout 700 Å. In one embodiment the thickness of the reflective layer isin between about 300 Å and about 600 Å. Suitable reflective layersinclude, but are not limited to, aluminum, silver, gold, titanium, andalloys and mixtures comprising at least one of the foregoing. Inaddition to the data storage layer(s), dielectric layer(s), protectivelayer(s), and reflective layer(s), other layers can be employed such aslubrication layer(s), adhesive layer(s) and others. Suitable lubricantlayers include, but are not limited to, fluoro compounds such as fluorooils and greases.

[0017] In the context of the present disclosure, a typical data storagemedium further comprises at least one high modulus layer (part 40 inFIG. 1; part 100 in FIG. 2). In one embodiment of the presentdisclosure, a suitable high modulus layer typically comprises athermoset polymer, which can be cured thermally, cured by ultraviolet(UV) radiation, or cured by any method commonly known to those skilledin the art. In another embodiment of the present disclosure, the highmodulus layer comprises a thermoplastic polymer. In yet anotherembodiment of the present disclosure, the high modulus layer comprises acombination of a thermoset polymer and a thermoplastic polymer.Typically, the high modulus layer is applied to the storage medium via aspin-coating process, however, any method known to those skilled in theart such as, but not limited to, spray deposition, sputtering, andplasma deposition can be used to deposit a high modulus layer with athickness in a range between about 0.5 micron and about 30 microns ontothe data storage medium. Illustrative examples of thermoset polymersinclude, but are not limited to, polymers derived from silicones,polyphenelene ethers, epoxys, cyanate esters, unsaturated polyesters,multifunctional allylic materials, diallylphthalate, acrylics, alkyds,phenol-formaldehyde, novolacs, resoles, bismaleimides,melamine-formaldehyde, urea-formaldehyde, benzocyclobutanes,hydroxymethylfurans, isocyanates, and any combinations thereof. In oneembodiment, the thermoset polymer further comprises at least onethermoplastic polymer, such as, but not limited to, polyphenylene ether,polyphenylene sulfide, polysulfone, polyetherimide, or polyester.Typically, the high modulus layer is a copolycarbonate ester. Thethermoplastic polymer is typically combined with a thermoset monomermixture before curing of said thermoset. In addition the high moduluslayer may be added during the lamination process of the pressuresensitive adhesive.

[0018] Currently, the dimensions of the storage medium are specified bythe industry to enable their use in presently available data storagemedium reading and writing devices. The data storage medium typicallyhas an inner diameter in a range between about 15 mm and about 40 mm andan outer diameter in a range between about 65 mm and about 130 mm, asubstrate thickness in a range between about 0.4 mm and about 2.5 mmwith a thickness up to about 1.2 mm typically preferred. Other diametersand thickness may be employed to obtain a stiffer architecture ifnecessary.

[0019] The storage medium described herein can be employed inconventional optic, magneto-optic, and magnetic systems, as well as inadvanced systems requiring higher quality storage medium, areal density,or any combinations thereof. During use, the storage medium is disposedin relation to a read/write device such that energy (for instance,magnetic, light, electric, or any combination thereof) is in contactwith the data layer, in the form of an energy field incident on the datastorage medium. The energy field contacts the data layer(s) disposed onthe storage medium. The energy field causes a physical or chemicalchange in the storage medium so as to record the incidence of the energyat that point on a data layer. For example, an incident magnetic fieldmight change the orientation of magnetic domains within a data layer oran incident light beam could cause a phase transformation where thelight heats the point of contact on a data layer.

[0020] Numerous methods may be employed to produce the storage mediumincluding, but not limited to, injection molding, foaming processes,sputtering, plasma vapor deposition, vacuum deposition,electrodeposition, spin coating, spray coating, meniscus coating, datastamping, embossing, surface polishing, fixturing, laminating, rotarymolding, two shot molding, coinjection, over-molding of film,microcellular molding, and combinations thereof. In one embodiment, thetechnique employed enables in situ production of the substrate havingthe desired features, for example, pits and grooves. One such processcomprises an injection molding-compression technique where a mold isfilled with a molten polymer as defined herein. The mold may contain apreform or insert. The polymer system is cooled and, while still in atleast partially molten state, compressed to imprint the desired surfacefeatures, for example, pits and grooves, arranged in spiral concentricor other orientation, onto the desired portions of the substrate, i.e.,one or both sides in the desired areas. The substrate is then cooled toroom temperature.

[0021] The following examples are included to provide additionalguidance to those skilled in the art in practicing the claimedinvention. The examples provided are merely representative of thepresent disclosure. Accordingly, the following examples are not intendedto limit the invention, as defined in the appended claims, in anymanner.

EXAMPLES

[0022] Circular data storage disks were prepared as follows. A substratelayer of 4,4-isopropylidenediphenol-polycarbonate polymer (BPA-PC) wasmolded into circular disks about 1.1 mm thick, and with an inner radiusof about 15 mm and an outer radius of about 120 mm. A metallic datalayer, of about 500 Angstroms thick, was sputtered to one of thesurfaces of the BPA-PC substrate disks. Various thicknesses, describedin table 1, of an acrylic lacquer layer (Daicure SD-698) were spincoated onto the metallic data layer of the disks, and the lacquer wascured using UV radiation. A co-polycarbonate-ester thin film of about 75micron thickness, was bonded to the acrylic layer of the disks using a25 micron thickness pressure sensitive adhesive of negligible modulus,to yield circular data storage disks with a layer configuration similarto that disclosed in FIG. 2. The data storage disks were equilibrated inan environment of an humidity of about 50%. The data storage disks werethen transferred from this first environment of an initial humidity ofabout 50%, to a second environment with humidity of about 90%. The tiltof the data storage disks was measured over time at a radius of 55 mmwhile the disk equilibrated in the 90% humidity. The results of themaximum radial tilt measured over the dynamic as the disksre-equilibrated to the 90% humidity environment for the data storagedisks with varying thickness of the spin-coated high modulus layer aredescribed in table 1. TABLE 1 Maximum High Modulus Radial tilt atLacquer thickness 55 mm (microns) (degrees) 0 0.316 6.6 0.196 14.6 0.12727.1 −0.171

[0023] As disclosed by the results in table 1, the addition of the highmodulus lacquer layer to the data storage disks reduces the radialtilt-of the disks during the dynamic period during which the datastorage disks are equilibrating from the first to the second humiditylevel.

[0024] While the invention has been illustrated and described, it is notintended to be limited to the details shown, since various modificationsand substitutions can be made without departing in any way from thespirit of the present disclosure. As such, further modifications andequivalents of the invention herein disclosed can occur to personsskilled in the art using no more than routine experimentation, and allsuch modifications and equivalents are believed to be within the spiritand scope of the disclosure as defined by the following claims.

What is claimed is:
 1. An asymmetric optical storage medium comprising alayer, which improves directional stability in said medium.
 2. Theoptical storage medium of claim 1, wherein said layer is a high moduluslayer.
 3. The optical storage medium of claim 2, wherein said highmodulus layer comprises a material that can be cured using ultra-violetlight.
 4. The optical storage medium of claim 3, wherein said materialcomprises at least one member selected from the group consisting of anacrylate, an epoxy, a silicone-acrylate, a urethane, and any combinationthereof.
 5. The optical storage medium of claim 2, wherein said highmodulus layer comprises a material that can be thermally cured.
 6. Theoptical storage medium of claim 5, wherein said material comprises atleast one member selected from the group consisting of a siliconehardcoat, silica with hydrolizable silanes, an epoxy, a urethane, animide, a siloxane and any combination thereof.
 7. The optical storagemedium of claim 4, wherein said acrylate is at least one member selectedfrom the group consisting of a poly-methylmethacrylate, a methylmethacrylate-polyimide copolymer, a methyl methacrylate-siliconecopolymer, and any combination thereof.
 8. The optical storage medium ofclaim 2, wherein said high modulus layer is in direct contact with adata layer.
 9. The optical storage medium of claim 2, wherein said highmodulus layer is in direct contact with a film layer.
 10. The opticalstorage medium of claim 2, wherein the thickness of said high moduluslayer is between about 0.01 micrometers (μm) and about 50 micrometers(μm).
 11. The optical storage medium of claim 2, wherein the said highmodulus layer has a modulus that is greater or equal to the modulus ofthe substrate.
 12. An asymmetric optical storage medium comprising thefollowing layers: at least one substrate layer; at least one data layerwhich is in direct contact with said substrate layer; at least one highmodulus layer which in direct contact with said data layer; and at leastone thin film layer which is in direct contact with said high moduluslayer.
 13. The optical storage medium of claim 12, wherein saidsubstrate layer is a polymeric material comprising at least one memberselected from the group consisting of a thermoplastic, a thermoset, andany combination thereof.
 14. The optical storage medium of claim 13,wherein said thermoplastic is one member selected from the groupconsisting of a polyester, a polycarbonate, a polystyrene, apolymethylmethacrylate, a polyketone, a polyamide, an aromaticpolyether, a polyether-sulfone, a polyether-imide, a polyether ketone, apolyphenylene ether, a polyphenylene sulfide, and any combinationsthereof.
 15. The optical storage medium of claim 12, wherein said datalayer comprises at least one member selected from the group consistingof a thermoplastic, a thermoset, and any combination thereof.
 16. Theoptical storage medium of claim 12, wherein said high modulus layercomprises at least one member selected from the group consisting of athermoplastic, a thermoset, and any combination thereof.
 17. The opticalstorage medium of claim 12, wherein said thin film layer comprises atleast one member selected from the group consisting of a homopolymer, acopolymer, a thermoplastic, a thermoset, and any mixtures thereof. 18.The optical storage medium of claim 17, wherein said thermoset is spincoated.
 19. A method for decreasing the tilt of an asymmetric opticalstorage medium, said method comprising an addition step wherein a highmodulus layer is added to an optical storage medium so that thedirectional stability of said medium is increased.
 20. The method ofclaim 19, wherein said optical storage medium comprises: at least onesubstrate layer; at least one data layer which is in direct contact withsaid substrate layer; at least one high modulus layer which in directcontact with said data layer; and at least one thin film layer which isin direct contact with said high modulus layer.